Merge tag 'random-6.0-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random

Pull random number generator updates from Jason Donenfeld:
 "Though there's been a decent amount of RNG-related development during
  this last cycle, not all of it is coming through this tree, as this
  cycle saw a shift toward tackling early boot time seeding issues,
  which took place in other trees as well.

  Here's a summary of the various patches:

   - The CONFIG_ARCH_RANDOM .config option and the "nordrand" boot
     option have been removed, as they overlapped with the more widely
     supported and more sensible options, CONFIG_RANDOM_TRUST_CPU and
     "random.trust_cpu". This change allowed simplifying a bit of arch
     code.

   - x86's RDRAND boot time test has been made a bit more robust, with
     RDRAND disabled if it's clearly producing bogus results. This would
     be a tip.git commit, technically, but I took it through random.git
     to avoid a large merge conflict.

   - The RNG has long since mixed in a timestamp very early in boot, on
     the premise that a computer that does the same things, but does so
     starting at different points in wall time, could be made to still
     produce a different RNG state. Unfortunately, the clock isn't set
     early in boot on all systems, so now we mix in that timestamp when
     the time is actually set.

   - User Mode Linux now uses the host OS's getrandom() syscall to
     generate a bootloader RNG seed and later on treats getrandom() as
     the platform's RDRAND-like faculty.

   - The arch_get_random_{seed_,}_long() family of functions is now
     arch_get_random_{seed_,}_longs(), which enables certain platforms,
     such as s390, to exploit considerable performance advantages from
     requesting multiple CPU random numbers at once, while at the same
     time compiling down to the same code as before on platforms like
     x86.

   - A small cleanup changing a cmpxchg() into a try_cmpxchg(), from
     Uros.

   - A comment spelling fix"

More info about other random number changes that come in through various
architecture trees in the full commentary in the pull request:

  https://lore.kernel.org/all/20220731232428.2219258-1-Jason@zx2c4.com/

* tag 'random-6.0-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random:
  random: correct spelling of "overwrites"
  random: handle archrandom with multiple longs
  um: seed rng using host OS rng
  random: use try_cmpxchg in _credit_init_bits
  timekeeping: contribute wall clock to rng on time change
  x86/rdrand: Remove "nordrand" flag in favor of "random.trust_cpu"
  random: remove CONFIG_ARCH_RANDOM

5 files changed, 31 insertions, 96 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5aa4c2ecf5c7..1e419d1581bc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1812,15 +1812,6 @@ config ARCH_USES_PG_UNCACHED
 	def_bool y
 	depends on X86_PAT
 
-config ARCH_RANDOM
-	def_bool y
-	prompt "x86 architectural random number generator" if EXPERT
-	help
-	  Enable the x86 architectural RDRAND instruction
-	  (Intel Bull Mountain technology) to generate random numbers.
-	  If supported, this is a high bandwidth, cryptographically
-	  secure hardware random number generator.
-
 config X86_UMIP
 	def_bool y
 	prompt "User Mode Instruction Prevention" if EXPERT
diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
index ebc248e49549..02bae8e0758b 100644
--- a/arch/x86/include/asm/archrandom.h
+++ b/arch/x86/include/asm/archrandom.h
@@ -31,20 +31,6 @@ static inline bool __must_check rdrand_long(unsigned long *v)
 	return false;
 }
 
-static inline bool __must_check rdrand_int(unsigned int *v)
-{
-	bool ok;
-	unsigned int retry = RDRAND_RETRY_LOOPS;
-	do {
-		asm volatile("rdrand %[out]"
-			     CC_SET(c)
-			     : CC_OUT(c) (ok), [out] "=r" (*v));
-		if (ok)
-			return true;
-	} while (--retry);
-	return false;
-}
-
 static inline bool __must_check rdseed_long(unsigned long *v)
 {
 	bool ok;
@@ -54,48 +40,23 @@ static inline bool __must_check rdseed_long(unsigned long *v)
 	return ok;
 }
 
-static inline bool __must_check rdseed_int(unsigned int *v)
-{
-	bool ok;
-	asm volatile("rdseed %[out]"
-		     CC_SET(c)
-		     : CC_OUT(c) (ok), [out] "=r" (*v));
-	return ok;
-}
-
 /*
  * These are the generic interfaces; they must not be declared if the
- * stubs in <linux/random.h> are to be invoked,
- * i.e. CONFIG_ARCH_RANDOM is not defined.
+ * stubs in <linux/random.h> are to be invoked.
  */
-#ifdef CONFIG_ARCH_RANDOM
 
-static inline bool __must_check arch_get_random_long(unsigned long *v)
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
 {
-	return static_cpu_has(X86_FEATURE_RDRAND) ? rdrand_long(v) : false;
+	return max_longs && static_cpu_has(X86_FEATURE_RDRAND) && rdrand_long(v) ? 1 : 0;
 }
 
-static inline bool __must_check arch_get_random_int(unsigned int *v)
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
 {
-	return static_cpu_has(X86_FEATURE_RDRAND) ? rdrand_int(v) : false;
+	return max_longs && static_cpu_has(X86_FEATURE_RDSEED) && rdseed_long(v) ? 1 : 0;
 }
 
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
-{
-	return static_cpu_has(X86_FEATURE_RDSEED) ? rdseed_long(v) : false;
-}
-
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
-{
-	return static_cpu_has(X86_FEATURE_RDSEED) ? rdseed_int(v) : false;
-}
-
-extern void x86_init_rdrand(struct cpuinfo_x86 *c);
-
-#else  /* !CONFIG_ARCH_RANDOM */
-
-static inline void x86_init_rdrand(struct cpuinfo_x86 *c) { }
-
-#endif  /* !CONFIG_ARCH_RANDOM */
+#ifndef CONFIG_UML
+void x86_init_rdrand(struct cpuinfo_x86 *c);
+#endif
 
 #endif /* ASM_X86_ARCHRANDOM_H */
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 35d5288394cb..48276c0e479d 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -808,7 +808,7 @@ static void clear_rdrand_cpuid_bit(struct cpuinfo_x86 *c)
 		return;
 
 	/*
-	 * The nordrand option can clear X86_FEATURE_RDRAND, so check for
+	 * The self-test can clear X86_FEATURE_RDRAND, so check for
 	 * RDRAND support using the CPUID function directly.
 	 */
 	if (!(cpuid_ecx(1) & BIT(30)) || rdrand_force)
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c
index c4be62058dd9..26a427fa84ea 100644
--- a/arch/x86/kernel/cpu/rdrand.c
+++ b/arch/x86/kernel/cpu/rdrand.c
@@ -11,56 +11,39 @@
 #include <asm/archrandom.h>
 #include <asm/sections.h>
 
-static int __init x86_rdrand_setup(char *s)
-{
-	setup_clear_cpu_cap(X86_FEATURE_RDRAND);
-	setup_clear_cpu_cap(X86_FEATURE_RDSEED);
-	return 1;
-}
-__setup("nordrand", x86_rdrand_setup);
-
 /*
  * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
- * Run the instruction a few times as a sanity check.
- * If it fails, it is simple to disable RDRAND here.
+ * Run the instruction a few times as a sanity check. Also make sure
+ * it's not outputting the same value over and over, which has happened
+ * as a result of past CPU bugs.
+ *
+ * If it fails, it is simple to disable RDRAND and RDSEED here.
  */
-#define SANITY_CHECK_LOOPS 8
 
-#ifdef CONFIG_ARCH_RANDOM
 void x86_init_rdrand(struct cpuinfo_x86 *c)
 {
-	unsigned int changed = 0;
-	unsigned long tmp, prev;
-	int i;
+	enum { SAMPLES = 8, MIN_CHANGE = 5 };
+	unsigned long sample, prev;
+	bool failure = false;
+	size_t i, changed;
 
 	if (!cpu_has(c, X86_FEATURE_RDRAND))
 		return;
 
-	for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
-		if (!rdrand_long(&tmp)) {
-			clear_cpu_cap(c, X86_FEATURE_RDRAND);
-			pr_warn_once("rdrand: disabled\n");
-			return;
+	for (changed = 0, i = 0; i < SAMPLES; ++i) {
+		if (!rdrand_long(&sample)) {
+			failure = true;
+			break;
 		}
+		changed += i && sample != prev;
+		prev = sample;
 	}
+	if (changed < MIN_CHANGE)
+		failure = true;
 
-	/*
-	 * Stupid sanity-check whether RDRAND does *actually* generate
-	 * some at least random-looking data.
-	 */
-	prev = tmp;
-	for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
-		if (rdrand_long(&tmp)) {
-			if (prev != tmp)
-				changed++;
-
-			prev = tmp;
-		}
+	if (failure) {
+		clear_cpu_cap(c, X86_FEATURE_RDRAND);
+		clear_cpu_cap(c, X86_FEATURE_RDSEED);
+		pr_emerg("RDRAND is not reliable on this platform; disabling.\n");
 	}
-
-	if (WARN_ON_ONCE(!changed))
-		pr_emerg(
-"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
-
 }
-#endif
diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index 4fe7af58cfe1..9417d5aa7305 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -100,7 +100,7 @@ static void init_espfix_random(void)
 	 * This is run before the entropy pools are initialized,
 	 * but this is hopefully better than nothing.
 	 */
-	if (!arch_get_random_long(&rand)) {
+	if (!arch_get_random_longs(&rand, 1)) {
 		/* The constant is an arbitrary large prime */
 		rand = rdtsc();
 		rand *= 0xc345c6b72fd16123UL;